During the coming year we hope to obtain sufficient quantities of T cell suppressor factors to initiate their detailed characterization both as to structure and biological function. We have previously shown the existence of T cell-derived suppressor factors with either idiotypic or antiidiotypic binding sites. It should be of great interest to isolate and compare these two types of product. Our approach will be to prepare T cell hybridomas elaborating each of the two kinds of suppressor factor. Once these materials are available in quantity their biological and physical properties can be studied in much greater detail than is feasible at present. We will also continue studies on the degree of heterogeneity of A/J anti-Ar antibodies which share a common cross-reactive idiotype. This will be done by preparing additional monoclonal antibodies and characterizing them serologically, particularly with respect to public (shared) and private idiotypic determinants. In some instances amino acid sequence analysis may be carried out. These studies, combined with investigations at the level of DNA now being pursued in a collaborative study, should give us a clearer indication as to the size of the repertoire of anti-Ar antibodies bearing the cross-reactive idiotype in the A/J strain, and should permit a comparison with the number of inherited genes that control molecules expressing the idiotype.